The objectives of this project are to elucidate biochemical mechanisms controlling the synthesis, storage, release, action and termination of action of norepinephrine in the adrenergic neurons and how to assess these in the intact animal. 6-Fluoronorepinephrine is a substitute transmitter for norepinephrine and 6-fluorodopamine can replace dopamine in brain. Use of 6-fluoradopa as a precursor for these false transmitters is being evaluated. By blocking extra-junctional Alpha2-adrenoceptors the concentration of norepinephrine at Alpha1-adrenoceptors in the sympathetic neuronal-vascular smooth muscle junction has been estimated at between 10 to the -8 and 10 to the -6 m depending on the frequency of neuronal stimulation.